Method of ultrasonic scanning of bodies

ABSTRACT

In the illustrated embodiment, ultrasonic transmitter/receiver elements are arranged along a curved formation within a housing containing a coupling medium which is a good conductor of ultrasonic energy (for example a water medium) and are successively excited to direct ultrasonic beam energy via the coupling medium to an ultrasonic window of the housing. The transducer elements are mounted at different angular orientations such that their beam paths converge external to the ultrasonic window. The curvature of a carrier for the transducer elements may be controlled to adjust the distance of the point of convergence beyond the window without changing the length of the acoustic path in the coupling medium, or the transducer elements and/or ultrasonic window may be bodily shifted to simultaneously change the length of the acoustic path and the distance of the convergence point beyond the window. Internal body regions accessible through narrow acoustic apertures at varying depths dependent on individual body characteristics may thus be reached for scanning by appropriate adjustment of the depth of the convergence point of the ultrasonic beam paths, the diverging beam paths beyond such depth providing for a sector scanning configuration within the desired body region.

BACKGROUND OF THE INVENTION

The invention concerns an ultrasonic applicator for ultrasonic scanningof internal body regions, particularly for the purpose of obtainingultrasonic echo sectional views, with an ultrasonictransmitting/receiving system consisting of a plurality of ultrasonictransmitter/receiver elements, which are arranged adjacent one anotherand which can be activated in chronological succession.

An ultrasonic applicator of this type is prior art, wherein theindividual ultrasonic transmitter/receiver elements are arranged next toone another in one plane. During chronologically successive excitationof the individual transmitter/receiver elements, the ultrasonic beamenergy in the body area which is to be examined is shifted parallel toitself. Thus, the ultrasonic beam energy scans a body area along asuccession of mutually parallel lines. During the corresponding linearimaging of the ultrasonic echo signals received from each of thescanning lines, on the viewing screen of an oscilloscope, a sectionalview of the body region which is to be examined is obtained in thescanning plane.

Particularly in medical ultrasonic diagnosis, however, there are bodyregions of interest which are accessible from the body surface onlythrough relatively narrow acoustical apertures, such as, for example, inthe case of heart examinations, the intermediary spaces between theribs, or, in the case of skull examinations, thin bone areas at specificlocations at the top of the skull (calvarium); for example, the thinbone area above the ear. Ultrasonic scanning procedures which functionaccording to the principle of sector scanning would be advantageous forthe scanning of such body regions.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide anultrasonic applicator of the general type initially mentioned, but soconstructed that it permits of a sector scanning. The inventiveultrasonic applicator is to be such that a direct coupling of thecyclically scanning sound head on the body surface is avoided. Asidefrom the fact that direct coupling of a cyclically scanning sound headon the body surface, of a patient, for example, is not without problems,and moreover, that the vibration of an ultrasonic generator on the skinsurface may annoy the patient, the usual disturbances occurring inconnection with a direct coupling of a sound head are present. Suchdisturbances include, for example, the problem of multiple echos, whichoccur between strongly reflective boundary surfaces of the body and thesound head application surface, and which, as superimposed points oflight in the ultrasonic echo sectional view, make difficult thediagnostic evaluation of the sectional view. In addition, ambiguitiesdue to minor lobes may also result, and there is the disadvantage ofdead zones in the coupling area, since the direct coupling of a strongtransmission pulse prevents an echo reading from this close range. Anadditional disturbing disadvantage would result in the case of adirectly coupled sector scanning field, since the origin of thedivergent scanning lines would be in front of, or on, the body surface,respectively. If the access aperture for acoustical energy is located inthe interior of the body, such as, for example, in the space between theribs, which under certain circumstances may lie within the body at adepth of up to several centimeters, the potential advantage of sectorscanning with direct coupling is realized only to a very limited extent.

According to the present invention, the problem is solved in thatultrasonic transmitter and receiver elements are arranged in bent orcurved formation in a housing containing a coupling medium which is agood conductor for the ultrasonic energy, for example water, thearrangement of the transducer elements being such that duringchronologically successive excitation, the transducers direct ultrasonicbeam energy through an ultrasonic window in the housing for convergenceat a point outside of the housing, which point is common to all beampath directions.

In the ultrasonic applicator as specified by the invention, the targetpoint may be shifted to varying locations outside of the housingaccording to the selection of the distance between thetransmitter/receiver elements and the ultrasonic window in theapplicator housing, and with a corresponding curvature of the ultrasonictransmitter/receiver formation, the point of convergence (serving asorigin for the desired sector scanning field) may be shifted to anyselected location within the body. Thus, the sector scanning proceduremay also be applied with good success in the case of deeply-locatedacoustical bone openings. The arbitrarily selectable shifting of theintersection point, however, also makes possible the introduction of aprecursory acoustic path in the coupling medium between the ultrasonictransmitting/receiving system and the body surface. If this precursorypath is maintained acoustically only slightly longer than the maximumpenetration depth of the ultrasonic energy in the body, multiple echosbetween the sound head and the body tissue are then suppressed to agreat extent in a known manner. In addition, there is also no dead zone,and the ambiguities due to minor lobes are reduced to a minimum.

According to further advantageous features of the invention, means areprovided for changing the curvature of the transmitter/receiverformation so as to change the target point location within the bodyunder examination, and further to change the angle between the scanninglines where they diverge from the target point to define the sectorscanning field. This adjustment of the location of the origin point forthe diverging scanning lines may thus be effected without an appreciablechange in the length of the precursory coupling path between thetransducer system and the applicator window. According to furtheradvantageous features of the invention, adjustment means are present inorder to adjust the distance between the ultrasonic transducer systemand the ultrasonic window of the applicator so as to selectively adjustthe position of the target point external to the applicator and toadjust the effective length of the precursory acoustic path. Accordingto further specific features of the invention, the transducer elementsare arranged in a circular arc formation with the transducer elementsarranged to direct pulses of beam energy along respective beam pathswhich intersect at the center of curvature of the circular arcformation.

Other objects, features and advantages of the present invention will beapparent from the following detailed description taken in connectionwith the accompanying sheet of drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 illustrates the basic construction of an embodiment of ultrasonicapplicator according to the present invention and comprises a partialdiagrammatic longitudinal sectional view of the applicator in couplingrelation to a body surface for purposes of medical diagnosticexamination of an internal body region; and

FIG. 2 is a perspective view illustrating a preferredtransmitting/receiving system for the applicator of FIG. 1, and showingthe arcuate formation of the transducer elements.

DETAILED DESCRIPTION

FIG. 1 illustrates a housing 1 of an applicator having an interior spacefilled with an ultrasonic coupling medium, for example degasseddistilled water. An ultrasonic transmitting/receiving system is disposedin the housing and comprises a plurality of ultrasonic transducers 4arranged in circular arc formation on a carrier strip 3 (consisting ofepoxy resin provided with filler ingredients, for example). Thetransducer elements 4 preferably consist of barium titanate or leadzirconate. Depending upon choice, transducer elements 4 may exhibitplanar radiation surfaces or, for an improved beam focusing, they mayalso exhibit radiation surfaces which are curved along their lengthdimension as viewed in FIG. 2, the length dimension of the transducerelements 4 being transverse to the longitudinal dimension of the carrierstrip 3 as shown in FIG. 2. A common cable connection 5 connects theindividual transducer elements 4 to an electric transmitting andreceiving circuit (not shown), such circuit being coupled to anoscilloscope tube in an ultrasonic echo sectional display device fordisplaying echo signals received by the successive individual transducerelements 4. During chronologically successive excitation of transducerelements 4 by means of a corresponding sequential switching operation inthe transmitting and receiving circuitry, the ultrasonic beam of eachtransducer 4 is directed through an ultrasonic window 6 (a sealingmembrane which permits the ultrasonic energy to pass therethrough to theexterior of the applicator) and to a common target point 7 which is theintersection point of the ultrasonic beam paths associated with therespective transducer elements 4. The intersection point 7 is shown, forexample, as being located at a selected depth within an object underexamination which is indicated by reference numeral 8. Target point 7corresponds to the center of curvature of the circular arc-shapedarrangement of transducer elements 4. Thus, point 7 is equidistant fromthe radiation surfaces of each of the transducer elements 4 and each ofthe transducer elements may direct essentially unidirectional ultrasonicenergy along a beam path intersecting point 7. In FIG. 1, the ultrasonicbeam path of the uppermost ultrasonic transducer 4 is indicated byreference numeral 9. The ultrasonic beam path of the lowest transducerelement is designated by reference numeral 10, and is illustrated inbroken lines. The beam paths 9 and 10 define the boundaries of a sectorfield 7', and the beam energy diverging from point 7 thus provides ascanning sector field which may be scanned by the ultrasonic beam energyfrom the ultrasonic transmitting/receiving system 2.

In order to shift the intersection points 7 of the ultrasonic beam pathsof the individual transducer elements 4 to any selected depth in theobject under examination, 8, the interval between the ultrasonictransmitting/receiving system 2 and the ultrasonic window 6 in theapplicator housing 1 need only be correspondingly changed. For thispurpose, for example, the ultrasonic transmitting/receiving system issecured to a supporting member 11, and the member 11 is arranged to belongitudinally slidably adjustable in the directions of thedouble-headed arrow 13 in a guide groove 12 at the base of thehousing 1. A rotary knob 14 (indicated in dotted lines, for example),and located outside of applicator housing 1, serves the purpose ofshifting the transmitting/receiving system 2, the rotary knob 14 beingoperable to adjust the rotational position of a pinion 15 which isengaged with the teeth of a rack 16 secured to the supporting member 11.By selecting the direction of rotational adjustment of the rotary knob14, the transmitting/receiving system 2 can be moved toward or away fromthe ultrasonic window 6. The intersection point 7 of the beam paths ofthe transducers 4 is thereby shifted correspondingly more or less deeplybelow the surface of object 8. The adjustment means 11 through 16 forthe ultrasonic transmitting/receiving system 2, which is manuallyoperable, has been shown solely for the sake of example. Rotary knob 14may, for example, be replaced by a rotary motor, for example a steppingrotary motor. By correspondingly controlling an energizing button forsuch a rotary stepping motor, the transmitting/receiving system 2 may bedriven into a desired position at a desired longitudinal distance fromthe ultrasonic window 6. Changes in the acoustic path length between thetransmitting/receiving system 2 and the membrane window 6, for thepurpose of shifting the target point 7, however, may also be achieved,for example, by the provision of a membrane window means accommodatinglongitudinal adjustment of window 6 relative to the remainder of theapplicator housing, while the transmitting/receiving system 2 remainsfixed. For example, the fixed part of the applicator housing mayterminate in an open tubular part, and this tubular part may receive inoverlapping relation a closely fitting tubular part with membrane 6 atits outer end. Thus, the longitudinally adjustable membrane tube may bemoved toward or away from the transducer assembly 2 while maintaining asealing relation to the fixed part of housing 1. Such a modification ofthe window 6 to provide a longitudinally adjustable membrane tube, forexample, is to be included as part of the present invention.

In a practical exemplary embodiment according to FIG. 2, thetransmitting/receiving system 2 should preferably comprise all togetherapproximately one-hundred (100) transducer elements 4. The individualtransducer elements 4 should exhibit a width of one millimeter (1 mm)and a length of approximately five to ten millimeters (5 to 10 mm). Theinterval from the center of one transducer element 4 to the center ofthe adjacent transducer element 4 (median transducer interval) should beat a desired value in the range from approximately one to approximatelyone and five-tenths millimeters (1 to 1.5 mm). A value between aboutone-hundred millimeters (100 mm) and about one-hundred and fiftymillimeters (150 mm) is recommended as the radius of curvature of theentire transducer arrangement.

It will be apparent that many modifications and variations may beeffected without departing from the scope of the novel concepts of thepresent invention.

I claim as my invention:
 1. The method of scanning internal body regionsaccessible through narrow acoustic apertures, whichcomprises:sequentially directing ultrasonic beams from successivedirections toward substantially a common point of convergence at anarrow acoustic aperture within the body such that the beams extendthrough the acoustic aperture and then diverge along successive scanlines forming a sector scanning configuration within an internal bodyregion beyond the acoustic aperture, and predominantly utilizingultrasonic echo signals produced in the sector scanning configurationbeyond the point of convergence so as to predominantly provide anultrasonic echo sectional view of the internal body region beyond suchacoustic aperture.
 2. The method of scanning internal body regionsaccessible through narrow acoustic apertures, whichcomprises:sequentially directing ultrasonic beams through a bodyexternal surface from successive directions toward substantially acommon point of convergence at a narrow acoustic aperture within thebody and at a depth of up to several centimeters below the body externalsurface such that the beams extend through the acoustic aperture andthen diverge along successive scan lines forming a sector scanningconfiguration within an internal body region beyond the acousticaperture, and predominantly utilizing ultrasonic echo signals producedin the sector scanning configuration beyond the point of convergence soas to predominantly provide an ultrasonic echo sectional view of theinternal body region beyond such acoustic aperture.